Just like neon, argyle compression socks and the phrase "beast mode,” WOD, workout of the day, originally started with CrossFit and has since spread to the greater fitness population. A WOD (pronounced "wad") is simply a list of the exercises you're supposed to do that day. Gyms that use WODs generally put up a new one every 24 hours so you get concise instructions and a lot of training variety. But if you don't like it, just don't get your panties in a WOD. (Couldn’t resist.)

Another one you can expect to hear in a CrossFit box: AFAP, as fast as possible. The instructor gives you a certain number of reps to do for each exercise, and your goal is to finish quickly.

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VO2 Max

What it stands for: volume of oxygen (O2) maximum

Curious to know how your fitness level stacks up against someone like Lance Armstrong? Or maybe just your neighbor in spin class? While you can't quantify overall fitness, VO2 max is the number that remains supreme among endurance athletes. Known as the “Darth Vader test,” you find your VO2 max by sprinting on a treadmill with an air-tight face mask that measures the maximum amount of oxygen you can utilize during full-out exercise. For a woman in her 20s or 30s, the average VO2 max is between 30 to 35 percent—anything over 40 is considered excellent. Still curious about Lance? His is 85. Yeah…

A heart rate monitor (HRM) is one of the most common and informative devices a fit girl can have. The monitor, which measures how fast your heart is beating, often straps around your chest and sends a signal to a watch (or sometimes a sensor on your treadmill or spin bike) which then shows you the number. Why is this number useful to know? Read the next slide on BPM to find out!

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BPM

What it stands for: beats per minute

Knowing your heart rate, measured in BPM, is useful for monitoring how hard your body is truly working and calculating things like calories burned and how many of those calories came from fat. You can use an electronic gadget like a HRM (heart rate monitor) to determine your heart rate, or you can use the age-old method of pressing your fingers to your jugular or the back of your wrist, counting the beats in ten seconds, and then multiplying by six.

Metabolic testing is the most accurate way to determine what your BPM should be at certain points during your workout, but you can also calculating your target heart rate with a formula called the "heart rate reserve" method. Here’s how:
1. Determine your maximum heart rate (MHR) by subtracting your age from 220.
2. Subtract your resting heart rate (it's best to take this when you first wake up in the morning, using the method described above) from your maximum heart rate to find your heart rate reserve (HRR).
3. Multiply your HRR by the percentage of your MHR at which you wish to train (60 to 85 percent is the usual range for people looking to increase fitness and health).
4. Add your resting heart rate back to that result to get your target rate.

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AT

What it stands for: aerobic threshold

Lactic acid, despite what you may have heard, is not the source of all evil (i.e. soreness) in exercise. (Also note: It cannot be "worked out" by stretching or light cardio.) It turns out this misunderstood acid is a byproduct produced by our bodies as they switch from making energy aerobically (with oxygen) to making energy anaerobically (without oxygen). As we increase our exercise intensity, our bodies become less able to use oxygen efficiently and thus switch to this secondary pathway. It's this point, measured in BPM (beats per minute), that defines your aerobic threshold (AT), sometimes referred to as your lactate threshold (LT).

Your AT is important to know because after you've reached that point, say 160 BPM, you can only sustain that level of exertion for a very limited amount of time. If you don't have a HRM (heart rate monitor), your approximate AT is still pretty easy to recognize. It's that point at which your legs feel like they're on fire, your lungs want to explode, and you know you can't run much further. Fun!

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BMR/RMR

What it stands for: basal metabolic rate/resting metabolic rate

"I have a slow metabolism!" It’s one of the most common laments heard from people trying to lose weight. But unfortunately you can’t draw this conclusion from personal observation alone (I ate a 6-ounce box of chocolates and gained two pounds while my roommate ate an entire Ferrier Roche tower and lost weight!) There is, however, a way to find out how slow—or efficient, as I like to say—your metabolism truly is.

Through metabolic testing, you can find a number known as your basal metabolic rate (BMR) which is how many calories your body uses each day to live and breathe. Your resting metabolic rate (RMR) is a similar measure that tells you how many calories your body uses at rest. (The difference between the two is that BMR is slightly more accurate and requires a more precise test, while RMR is more of an estimate but is easier to measure.)

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RPE

What it stands for: rate of perceived exertion

On a scale of one to 10, how hard do you push yourself during your workouts? That's RPE in a nutshell. A rating of one might be lying in corpse pose during yoga, while 10 is more like you being chased by zombies in your dreams after that Walking Dead marathon. Since it's all based on your own perception of how hard you’re working, RPE helps you decide when you need to push harder to see the results you want. (Want to try fun experiment? See how hardcore (or not) you are by ranking your RPE and then correlating it with the BPM readout on your HRM!).

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PR

What it stands for: personal record

When someone talks about a personal record (PR), also sometimes referred to as PB for personal best, it means they beat their best race time, lifted their heaviest weight, or otherwise topped their previous best effort in an activity. If there ever was an occasion for giving knuckles in the gym, it's a PR!

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AMRAP

What it stands for: as many reps as possible

Between the sets, reps, rest periods, repeats, etc., deciphering a workout routine designed by someone else can feel like running on the treadmill while trying to read the newspaper… in Cantonese. AMRAP, one acronym that’s known to stymie fitness newbies, is telling you to do “as many reps as possible” of a certain exercise. It’s also a sign that your workout was designed by a smart fitness professional who would rather have you do three pushups with perfect form than crank out 10 with sagging hips.

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WOD

What it stands for: workout of the day

Just like neon, argyle compression socks and the phrase "beast mode,” WOD, workout of the day, originally started with CrossFit and has since spread to the greater fitness population. A WOD (pronounced "wad") is simply a list of the exercises you're supposed to do that day. Gyms that use WODs generally put up a new one every 24 hours so you get concise instructions and a lot of training variety. But if you don't like it, just don't get your panties in a WOD. (Couldn’t resist.)

Another one you can expect to hear in a CrossFit box: AFAP, as fast as possible. The instructor gives you a certain number of reps to do for each exercise, and your goal is to finish quickly.

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RM

What it stands for: one-rep maximum

Few things in the gym are more exciting than finding out your one-rep maximum (RM) on a squat. It's guaranteed to make you feel like She-Ra, Princess of Power! Whether you're testing your progress in your back squat, chest press, or any other strength move, your 1RM is the maximum amount of weight you can safely lift with good form. Similarly, you can measure 5RM, the amount of weight you can safely lift for five reps, or any other number of reps you like. Just don't forget to write your RMs down. It’s an excellent way to track your progress!

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HIIT

What it stands for: high-intensity interval training

Some people add "simply" to their high-intensity interval training, putting an "s" in front of HIIT. And if you've ever tried one of these short-but-super-intense workouts (think Tabata drills) then you'll know why. While the benefits of HIIT are numerous (Check out the top 8 here), the feeling while doing them is killer. But like many fitness endeavors, the more you put into HIIT, the more you get out of it!

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ACE

What it stands for: American College on Exercise

There are many certifications a personal trainer can earn—as evidenced by the three lines of letters after his or her name on a business card—but one of the most common and respected comes from the American College on Exercise (ACE). The ACE exam requires personal trainers to pass an extensive written exam and to continue getting education certificates to maintain their license. While it's not the only certification out there, it's a good place to start when looking for a new trainer.

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A Few Fun (but Useful) Extras

VPL: visible panty lines
This is exactly what you think it is. Thanks to the advent of skinny jeans and body-con dresses, we're all too familiar with the perils of VPL. And now this phenomenon has made it's way into the gym. Whether you choose to go commando under your capris, thong-clad under your tights, or full granny-panty under your gym shorts is totally up to you and your comfort level of comfort—we’ll never tell!

LBC: little black capris
Just like every woman needs a little black dress that makes her look and feel fabulous, every fit girl needs the perfect pair of LBCs (or little black pants)!